A significant portion of the cost of manufacturing certain food products results from the labor costs and handling such products during manufacturing and/or packaging. For example, flexible, planar food products such as tortillas are generally discharged from an oven or other processing machine in a randomly spaced sequence. Some of these tortillas may be defective such as, for example, by containing holes or being misshaped or of improper size. After being discharged from the oven or other processing machine, the tortillas are visually inspected, and defective tortillas are manually removed. The remaining tortillas are then hand counted and stacked prior to being packaged. The labor costs incurred in manually inspecting, sorting out defective product, counting and stacking the tortillas is a significant portion of their manufacturing cost.
The requirement that the process of inspecting, sorting, counting, and stacking be done manually limits the speed at which tortillas can be packaged after being discharged from and oven.
In an attempt to eliminate or reduce the expense and speed limitations inherent in manual processing of tortillas, various devices for stacking and counting tortillas have been developed. One such device, disclosed in U.S. Pat. No. 4,006,831, discloses an apparatus for stacking tortillas in which tortillas are placed on a moving conveyor belt and then flung from that belt against aligning arms. The tortillas then fall into a stationary tray. When a predetermined number of tortillas have been stacked on the tray, the tray is lowered so that the tortillas can be removed by a moving conveyor belt after the aligning arms have been pivoted downwardly to allow the stack of tortillas to move with the belt. The apparatus disclosed in U.S. Pat. No. 4,006,831 does mechanize several tortilla processing steps that were previously performed manually. However, it is still somewhat limited in its ability to count and stack tortillas, and in the speed at which it can count and stack tortillas.
U.S. Pat. No. 4,530,632 discloses an improved counting and stacking device for tortillas which is capable of handling tortillas having a wider variety of characteristics at a faster rate than the device disclosed in U.S. Pat. No. 4,006,831. The device disclosed in U.S. Pat. No. 4,530,632 receives tortillas on a moving belt which, after passing through a counting station, makes a 180.degree. turn so that the tortillas are then carried on the underside of the belt. A vacuum holds the tortillas against the belt until they reach a discharge station. The tortillas then drop onto a stationary tray. After a predetermined number of tortillas have been dropped onto the tray, a conveyor belt is lifted to engage the stacked tortillas thereby removing the stack from the discharge tray. Since the conveyor belt removes the stack of tortillas in the direction opposite the direction that the tortillas are delivered to the tray, the time required to remove the tortillas from the tray before additional tortillas may be stacked is minimized. As a result, the throughput of the device disclosed in U.S. Pat. No. 4,530,632 is relatively high.
Although the device disclosed in U.S. Pat. No. 4,530,632 represents a significant improvement in the art, it nevertheless has a number of limitations. First, it has no provision for either inspecting the tortilla for defects or for sorting out defective tortillas prior to stacking. As a result, the tortillas must be inspected manually prior to reaching the counting and stacking device. If any defective tortillas are overlooked prior to reaching the counting and stacking device, they will be stacked along with the other tortillas since tortillas cannot be easily removed from the equipment prior to stacking. Removal of a defective tortilla from the stack of tortillas is possible, but the resulting stack would then contain less than the proper number of tortillas.
Another limitation of the device disclosed in U.S. Pat. No. 4,530,632 is the limited throughput of the device. Although the device disclosed in U.S. Pat. No. 4,530,632 is markedly faster than previous devices, it is nevertheless undesirably slow for many applications. One speed limiting factor is the time needed to remove the stack of tortillas from the discharge tray before additional tortillas can be stacked on that tray. More specifically, additional tortillas cannot be stacked on the discharge tray until the upper tortilla in the stack has cleared the path that the next tortilla would follow as it is dropped from the conveyor onto the discharge tray. Yet the speed at which the stack can be accelerated and then moved from the discharge tray without disturbing the stack is limited.
Another speed limiting factor arises from tolerances in the time required for a tortilla to travel on a conveyor belt from a counting or position measuring station to the point that the tortilla is discharged from a conveyor belt. The time required for a tortilla to travel from a counting or position measuring station to the discharge point is theoretically a constant function of the conveyor belt speed. However, tortillas traveling on a conveyor belt typically undergo some slippage on the belt because of such factors as air resistance. Thus, since the discharge type can vary somewhat, extra time must be allowed for removal of the stack of tortillas from beneath the discharge location.